I found a very interesting technique to coloring a brush.. Open New Document (Control + N) and choose a black as a background. First of all.. u must have a brush.. Pick a brush and splash it to your canvas. (Before that, create a new layer and splash it at the new layer.) Here i choose a fractal brush to demonstrate.
Now. Copy brush layer(drag a layer onto a 'new layer' symbol) and apply the gaussian blur, Filter > blur > gaussian blur.. and then reduce opacity to 40.
Create one layer.. name the layer as "color". on layer color pick a brush (B) and paint the layer with any different colour. Here I use a basic brush with soft mechanical size 150px. And I choose blue & pink color. (2 different color, 1 layer!)
After that. Create a new layer. (And press D). Go to Filter > Render > Clouds. Then Filter > Blur > Gaussian Blur (10px). Set the blending mode to 'vivid light' and reduce opacity to 50
Finally, on layer 'color', set the blending mode to 'overlay' and wallllap!! the result.